Flash lamp and lead-in wire therefor



July 31, 1956 R. M. ANDERSON FLASH LAMP AND LEAD-IN WIRE. THEREFOR Filed April 19, 1954 TigZ.

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lnven tov. liyobev i; M. Anderson, His Attovne3 United States Patent Oh FLASH LAMP AND LEAD-IN WIRE THEREFOR Robert M. Anderson, Euclid, Ohio, assignor to General Electric Company, a corporation of New York Application April 19, 1954, Serial No. 424,078

5 Claims. (CI. 67-31) My invention relates in general to flash lamps of the type comprising a sealed radiation-transmitting envelope of glass or other suitable material and containing a combustion-supporting gaseous filling and a readily combustible material which, upon ignition, produces a momentary flash of actinic light of high intensity suitable for picture taking purposes. More particularly, my invention relates to the mount structure and electric ignition means for such flash lamps, and in particular to the lead-in wires thereof.

Flash lamps of the type referred to are customarily provided with electric ignition means in the form of a fine ignition filament, such as a straight length of tungsten wire, disposed within the lamp envelope and connected across the inner lead portions of lead-in wires sealed through the glass stem of the lamp mount. The ignition filament is customarily connected to the lead-in wires either by being pressed flatwise into the sides of the wires, or by being inserted into laterally extending notches which are cut into the sides of the wires and are then closed by upsetting the metal of the wires around the filament to clamp it in place. Because of the extreme fineness (usually one mil or less in wire diameter) and consequent fragility of the ignition filaments customarily employed in such flash lamps, and also because of the customary omission, for cost-saving purposes, of any supplementary supports for the inner leads other than the anchorage thereof in the stem press, it is necessary that the filament-supporting inner lead portions of the lead-in wires possess suflicient rigidity or sturdiness to withstand the usual shocks and impacts incidental to the normal handling and use of the lamps without the said inner lead portions bending or deflecting so as to cause the breakage of the filament.

The lead-in wires commonly employed in flash lamps heretofore have been formed with inner lead portions constituted either of nickel or nickel plated iron wire. Because of the relatively hard character of such nickel or nickel-plated iron inner lead portions, a relatively high per cent of filament breakage occurs during the mounting or clamping of the filaments on the lead-in wires of the lamp mount. The entire lamp mount is thereby rendered defective and must be discarded, resulting in a relatively high and objectionable percentage of production rejects or so-called shrinkage. In addition, where the connection of the filaments to the lead-in wires is effected by the notching of the latter and the insertion and embedding of the filament in such notches, the use of lead-in wires having nickel or nickel-plated iron inner lead portions requires an appreciable amount of notching cutter maintenance owing to the hardness of such type inner leads.

It is an object of my invention, thereforefto provide,

a flash lamp of the character referred to and having an ignition filament mount structure of an improved construction which enables the manufacture thereof with a greatly reduced percentage of production rejects as compared to that heretofore experienced. 7

Another object of my invention is to provide a novel form of lead-in wire for flash lamps having an inner lead portion which is of the required rigidity to withstand Patented July 31, 1956 handling and use of the lamps without deflecting to such an extent as to break the lamp ignition filament but the surface layer of which is nevertheless sufliciently soft to enable the pressing and embedding of the filament in the said surface layer with a greatly reduced percentage of filament breakage as compared to that previously encountered.

In accordance with the invention, the above objects are attained by employing lead-in wires having their inner lead portions constituted of copper-clad iron or nickel wire the copper surface layer of which is of a thickness at least approximating the wire diameter of the filament which is to be clamped thereto. I

Further objects and advantages of my invention will appear from the following detailed description of species thereof and from the accompanying drawing.

In the drawing, Fig. 1 is an elevation of a flash lamp according to the invention.

Fig. 2 is an elevation of the composite lead-in wire of my invention.

Fig. 3 is a fragmentary sectional view, on a greatly enlarged scale, showing one form of connection of the lamp filament to the lead-in wire of my invention.

Fig. 4 is a fragmentary sectional view, on a greatly enlarged scale, showing a modified form of connection of the lamp filament to the lead-in Wire of my invention.

Referring to the drawing, the flash lamp there shown comprises a sealed radiationor light-transmitting envelope or bulb 1 of glass or other suitable material and having a neck portion 2. The bulb contains a quantity of readily combustible material 3 which, on ignition and combustion, produces a momentary flash of actinic light of high intensity suitable for picture taking purposes. In the particular case illustrated, the combustible material 3 is in the form of a loosely distributed quantity of filamentary material such as fine wire, or finely cut strands or ribbons of metal foil such as that commonly referred to as shredded foil. The filamentary combustible material 3 may be of any suitable composition such as, for example, aluminum or an aluminum-magnesium alloy containing a small percentage of magnesium. The bulb 1 also contains a filling of a suitable combustion-supporting gaseous medium such as oxygen at a suitable pressure.

Sealed into the neck end of the bulb 1 is a lamp mount 4 comprising a glass stem tube 5 fused to the outer end of the bulb neck 2 and having a press portion 6 through which are sealed a pair of lead-in wires 7. The said lead in wires 7 are connected at their outer ends one to the end contact 8 and the other to the metal shell or side contact 9 of a conventional type lamp base 10 suitably secured to the neck 2 of the bulb, as by conventional basing cement.

Connected to the inner ends of the lead-in wires 7 is an ignition filament 11 preferably in the form of a straight length of tungsten Wire having a wire diameter of at most one mil. The filament 11 is connected to the leadin wires 7 either by pressing it flatwise into the sides of the wires to embed it therein, as shown in Fig. 3, or by inserting the opposite ends of the filament into laterally extending notches cut in the sides of the lead-in wires and then pressing or upsetting the portions of the leadin wires at either side of the filament so as to force the metal of the inner leads against and around the outer sides of the filament ends and firmly embed them in the lead-in wires, as shown in Fig. 4. The ignition filament 11 is located within the mass of filamentary combustible material 3 so as to be within eifective ignition range thereof. The inner end portions of the lead-in wires 7 the physical shocks and impacts incident to normal are provided with coatings or small beads 12 of a suitable fulminating or primer material such as that described and claimedin U. S. Patent 2,280,598, Meridith, issued April 21, 1942, and assigned to 'theassignee of the present application. The ignition filament 11 and primer beads 3 12 together constitute the ignition means for the particular type of flash lamp illustrated in Fig. 1.

As shown in Fig. 2, the lead-in wires 7 are of the conventional three-part construction such as commonly employed in flash lamps and incandescent lamps, and they comprise an inner lead portion 13, an outer lead portion 14, and an intermediate press or seal lead portion 15, the three lead portions being butt-welded together in end-to-end relation to form a single composite wire.

The outer lead portion 14'may be constituted of anysuitable material, preferably copper, while the press lead portion 15 is constituted of a material having an expansion coeflicient more or less matching that of the glass of the stem tube 5 into which the press leads 15 are sealed. Thus, for the soft glasses customarily employed for the stem tubes 5 of flash lamps, the press leads 15 may be made of copper-clad nickel-iron alloy wire such as that commonly known as Dumet. To insure against cracking of the glass stem press 5 following the sealing of the lead-in wires 7 therethrough, the press leads 15 should b of a diameter of the order of 10 to mils. A wire diameter of around 12 mils, for example, for the press leads 15 has been found to be eminently satisfactory from this standpoint.

In accordance with the invention, the inner lead portions 13 of the lead-in wires 7 are constituted of a rigid wire core 16 formed of a suitable relatively hard material such as iron or nickel or alloys thereof (preferably iron), and having an outer surface layer or sheath 17 of a relatively soft or ductile material, such as copper, tightly bonded onto the core wire 16. Copper-clad iron wire such as that commercially available at present is admirably suited for use as the inner lead portion 13 of the lead-in wire. For the purposes of the invention, the

copper surface layer or sheath 17 should be of a thickness at least approximating that of the filament wire 11. Since the ignition filament 11, as stated above, is of a diameter at most of the order of one mil, the copper surfac layer 17 on the core wire 16 should therefore be of a thickness of at least one mil. However, since no apparent added advantage is obtained by employing a copper surface layer 17 of a thickness much in excess of 2 or 3 mils, a thickness range for the copper surface layer or sheath 17 of from 1 to 3 mils is therefore particularly suitable for the purposes of the invention. As a specific example, commercially available copper-clad iron wire, consisting of around to 40 per cent by weight of copper and 60 to 70 per cent by weight of iron, has been found to be entirely satisfactory.

In sealing the lead-in wires into the press portion 6 of the glass stem 5, a short section of the length of the inner leads 13, adjacent the joints or weld knots 18 between the press leads 15 and the inner leads 13, are also embedded in the glass of the stem press along with the press leads 15 themselves, in order to firmly anchor the said inner leads 13 in the stem press so as to be rigidly supported therefrom. To insure against cracking of the glass stem press 6 by these embedded portions of the inner leads 13, following the sealing of the lead-in wires into the stem press 6, it is preferred that the inner leads 13 be of a diameter less than 30 mils or so. In this connection, a range of wire diameters for the inner leads 13 of from 15 to 25 mils has been found to be particularly suitable from this standpoint while at the same time affording the necessary rigidity to prevent breakage of the filament from deflection of the inner leads by the impacts encountered in the normal handling and use of the lamp.

Fig. 3 illustrates one form of connection of the ignition filament 11 to the inner leads 13 of the lead-in wires 7 according to my invention. As there shown, the filament is pressed flatwise into the side of the inner lead 13 by suitable pressing jaws (not shown) which flatten out the inner lead to a reduced thickness, as indicated at 19, of the order of half the original wire diameter while at the same time forcing the filament wire 11 into the copper surface layer 17 of the inner leads so as to be firmly embedded therein. Because of the relatively soft character of the copper surface layer 17, the pressing of the hard tungsten filaments 11 thereinto is accomplished with a minimum amount of breakage of the filaments which is much lower than that heretofore experienced. Thus, whereas the percentage of production rejects or shrinkage from filament breakage on mounting by the above-described pressed-in method of connecting the filament to the inner leads 13 has been of the order of 1.0% when employing lead-in wires heretofore in general use, the percentage of production rejects or shrinkage from such cause when employing lead-in wires 7 according to the invention has been of the order of 0.1%, which amounts to only one-tenth as much shrinkage as before. Obviously, this constitutes an appreciable manufacturing economy.

In the modified form of connection shown in Fig. 4, the ends of the ignition filament 11 are first inserted in laterally extending notches cut in the sides of the inner leads 13 and then the metal of the inner leads, at each side of the filament lying in the notches, is upset by a suitable upsetting tool and forced against and around the outer end of the filament, as shown at 20, to thereby firmly embed and clamp the filament in place in the inner leads 13. Because of the relatively soft character of the copper surface layer 17 of the inner lead, this upsetting or filament-clamping operation, like the pressingin filament-clamping operation described above, can be carried out with a considerably lower percentage of filament breakage and production shrinkage as compared to that heretofore experienced when using nickel or nickelplated iron inner leads. Thus, whereas the percentage of filament breakage and resulting production shrinkage attributable to such type of filament-clamping procedure amounts to around 0.9% when employing inner leads of the type heretobefore in general use, the percentage of filament breakage and production shrinkage from such cause when employing lead-in wires 7 according to the invention is only around 0.1, which amounts to only around one-ninth as much shrinkage as before. This again represents an appreciable manufacturing economy. In addition, the soft surface layer 17 on the inner leads 13 of the lead-in wires according to the invention effects a very considerable reduction in the maintenance of the cutter which is used to cut the filament-receiving notches in the inner leads 13.

While I have shown and described the invention as applied to a flash lamp of the type employing combustible light-giving material of filamentary form such as wire or so-called shredded foil, it is obvious that the invention may be applied as well to flash lamps employing combustible material of other forms. Thus, it may be applied to flash lamps of the type employing, as the sole source of actinic light, combustible material in the form of coatings or small beads of a suitable fulminating material on the inner ends of the lead-in Wires, such as is employed in flash lamps of the co-called primer or SM type as disclosed and claimed in U. S. Patent 2,291,983, Pipkin, issued August 4, 1942, and assigned to the assignee of the present invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A flash lamp comprising a sealed radiation-transmitting envelope containing a combustion-supporting gaseous filling and a quantity of readily combustible material, and electric ignition means for said combustible material comprising a pair of lead-in wires sealed through the wall of and extending into said envelope, and an ignition filament of tungsten wire having a wire diameter at most of the order of one mil and disposed in said envelope and having its opposite ends firmly embedded in said lead-in Wires to electrically connect the filament thereto, at least the portion of each of said lead-in wires in which the filament is embedded being constituted of a copper-sheathed core Wire of a metal selected from the group consisting of iron and nickel and alloys thereof, said copper sheathing having a thickness at least substantially equal to the diameter of said filament wire and said filament wire being substantially embedded in and retained by said copper sheathing.

2. A flash lamp comprising a sealed radiation-transmitting envelope containing a combustion-supporting gaseous filling and a quantity of readily combustible material, and electric ignition means for said combustible material comprising a pair of lead-in wires sealed through the wall of and having inner lead portions extending into said envelope, and an ignition filament of tungsten wire having a wire diameter at most of the order of one mil and disposed in said envelope and having its opposite ends pressed into the sides of said inner lead portions to firmly embed the filament in and electrically connect it to the said inner lead portions, said inner lead portions of the lead-in wires being constituted of copper-clad iron wire, said copper surface layer on said copper clad iron wire having a thickness at least substantially equal to the diameter of said filament wire and said filament wire being substantially embedded in and retained by said copper surface layer.

3. A flash lamp comprising a sealed radiation-transmitting envelope containing a combustion-supporting gaseous filling and a quantity of readily combustible material, and electric ignition means for said combustible material comprising a pair of lead-in wires sealed through the wall of and having inner lead portions extending into said envelope and provided with notches in the sides there of, and an ignition filament of tungsten wire having a wire diameter of at most of the order of one mil and disposed in said envelope and having its opposite ends located in the said notches, the sides of said notches being pressed together and around the outer side of the filament therein to firmly embed the filament in the inner lead portions and electrically connect it thereto, said inner lead portions of the lead-in wires being constituted of copperclad iron wire, the copper surface layer of said copper clad iron wire having a thickness of at least substantially equal to the diameter of said filament wire and said fila ment wire being substantially embedded in and retained by said copper surface layer.

4. A flash lamp of the character set forth in claim 1 wherein the said copper sheath on the portions of the leadin wires in which the filament is embedded has a thickness of at least one mil.

5. A flash lamp comprising a sealed radiation-transmitting envelope containing a combustion-supporting gaseous filling and a quantity of readily combustible material, and electric ignition means for said combustible material comprising a pair of lead-in wires sealed through the wall of and having inner lead portions extending into said envelope, and an ignition filament of tungsten wire having a wire diameter at most of the order of one mil and disposed in said envelope and having its opposite ends firmly embedded in said inner lead portions to electrically connect the filament thereto, said inner lead portions of the lead-in Wires having a wire diameter of the order of 15 to 25 mils and being constituted of a copper-sheathed core wire of a metal selected from the group consisting of iron and nickel and alloys thereof, the copper sheath on said core wire having a thickness of from 1 to 3 mils, said filament wire being embedded in and retained by said copper sheath.

References Cited in the file of this patent UNITED STATES PATENTS 

